rcfile: process extensions to file-matching commands straightaway

When 'extendsyntax' is used with a 'header' or 'magic' command, it
must be processed immediately.  It is pointless to store the command,
because when then it is processed (when the syntax gets used), it is
too late to have any effect.

This fixes https://savannah.gnu.org/bugs/?56997.

With-help-from: Brand Huntsman <alpha@qzx.com>

Bug existed since version 4.3, commit cba9d8d0.

src/rcfile.c

@@ -1001,6 +1001,7 @@ void parse_rcfile(FILE *rcstream, bool just_syntax, bool intros_only)
 
 	while ((len = getline(&buffer, &size, rcstream)) > 0) {
 		char *ptr, *keyword, *option;
+		bool drop_open = FALSE;
 		int set = 0;
 		size_t i;
 
@@ -1032,6 +1033,7 @@ void parse_rcfile(FILE *rcstream, bool just_syntax, bool intros_only)
 		if (!just_syntax && strcasecmp(keyword, "extendsyntax") == 0) {
 			augmentstruct *newitem, *extra;
 			char *syntaxname = ptr;
+			char *argument;
 			syntaxtype *sint;
 
 			check_for_nonempty_syntax();
@@ -1047,12 +1049,23 @@ void parse_rcfile(FILE *rcstream, bool just_syntax, bool intros_only)
 				continue;
 			}
 
+			argument = strdup(ptr);
+			keyword = ptr;
+			ptr = parse_next_word(ptr);
+
+			/* File-matching commands need to be processed immediately;
+			 * other commands are stored for possible later processing. */
+			if (strcmp(keyword, "header") == 0 || strcmp(keyword, "magic") == 0) {
+				free(argument);
+				live_syntax = sint;
+				opensyntax = TRUE;
+				drop_open = TRUE;
+			} else {
 			newitem = nmalloc(sizeof(augmentstruct));;
 
-			/* Store the content of an 'extendsyntax', for later parsing. */
 			newitem->filename = strdup(nanorc);
 			newitem->lineno = lineno;
-			newitem->data = strdup(ptr);
+			newitem->data = argument;
 			newitem->next = NULL;
 
 			if (sint->augmentations != NULL) {
@@ -1064,6 +1077,7 @@ void parse_rcfile(FILE *rcstream, bool just_syntax, bool intros_only)
 				sint->augmentations = newitem;
 
 			continue;
+			}
 		}
 
 		/* Try to parse the keyword. */
@@ -1120,6 +1134,9 @@ void parse_rcfile(FILE *rcstream, bool just_syntax, bool intros_only)
 		else if (intros_only)
 			jot_error(N_("Command \"%s\" not understood"), keyword);
 
+		if (drop_open)
+			opensyntax = FALSE;
+
 		if (set == 0)
 			continue;